If you’re getting an error that reads something like “Cannot insert the value NULL into column ‘CatId’, table ‘demo.dbo.Cats’; column does not allow nulls. INSERT fails” in SQL Server, it’s because you’re trying to insert a NULL value into non-nullable column (i.e. a column with a NOT NULL constraint).
We can’t insert NULL values into non-nullable columns.
To fix this issue, insert a non-NULL value.
Continue readingDropping a primary key in any RDBMS is a critical operation that requires careful consideration, especially when there are related foreign keys in other tables.
The decision to drop a primary key is not to be taken lightly.
That said, this article walks through the process of how to drop a primary key in SQL Server, while highlighting important considerations.
Continue readingIf you’re getting an error that reads “An explicit value for the identity column in table ‘Dogs’ can only be specified when a column list is used and IDENTITY_INSERT is ON” in SQL Server, it appears that you’re trying to insert a value into an IDENTITY column.
Specifically, you’re trying to do that while the IDENTITY_INSERT option is set to OFF.
To fix this issue, either enable IDENTITY_INSERT before inserting the value, or omit the value from your list of values to insert (and let the IDENTITY column do it’s thing).
In PostgreSQL, both UNIQUE indexes and UNIQUE constraints can be used to enforce uniqueness on columns.
So you may be wondering; if that’s true, why have both? And are there any circumstances that we should choose one over the other?
Let’s find out.
Continue readingA UNIQUE constraint is a rule that we can apply to one or more columns in a database table to ensure that the values in those columns are unique across all rows.
In SQL Server we have a few options when it comes to creating a UNIQUE constraint. But it’s usually done when we create the table or alter it. That is, we include the constraint code in the CREATE TABLE statement or the ALTER TABLE statement.
We can also create a UNIQUE index, which can be used in place of the previous methods, but can have the same effect.
Let’s check out several ways to create a UNIQUE constraint in SQL Server.
Constraints are an important concept in relational database management systems (RDBMSs). Whenever we design a database, we need to ensure that it will be able to enforce data integrity, by checking or restricting what the user can enter to only data that conforms to the rules of the database. That’s where a constraint can help.
This article explores what SQL constraints are, the various types available, their importance, and how they are implemented.
Continue readingWhen working with PostgreSQL databases, you may sometimes need to clear out all the data from tables that have foreign key relationships. This process, known as truncation, can be tricky when dealing with interconnected tables.
By default, if we try to truncate a table that is referenced by another table via a foreign key constraint, we’ll get an error that looks something like this: “ERROR: cannot truncate a table referenced in a foreign key constraint“.
You may have encountered this before finding this article. However, all is not lost. Below are two options for overcoming this issue.
Continue readingIn SQL, constraints are essential for maintaining data integrity and ensuring the accuracy and reliability of the data stored within a database. One of the most commonly used constraints in SQL databases is the NOT NULL constraint.
In this article, I provide a quick overview of the NOT NULL constraint, its purpose, syntax, usage, and practical examples.
The DEFAULT constraint is a nifty little feature in SQL databases that simplifies data management by assigning default values to columns in a table. This can help us maintain data integrity in our databases.
Let’s take a look at the DEFAULT constraint.
In SQL Server, ON DELETE NO ACTION is an option that we can apply to foreign key constraints to prevent the deletion of a row in the parent table if there are related rows in the child table.
Unlike ON DELETE CASCADE, which would delete the related rows in the child table, NO ACTION enforces that if a deletion would result in orphaned records in the child table, the deletion operation is prohibited, and an error is raised.